In recent years, for example, digital interfaces such as HDMI (High Definition Multimedia Interface) have been widely used as a communication interface for sending data of images or voices from source devices to sink devices at high speed. The source devices are, for example, a mobile phone, a game machine, a DVD (Digital Versatile Disc) recorder or a set-top box, and in addition to the above, there is an AV source (Audio Visual source). The sink devices are, for example, a television receiver, a projector and in addition to the above there is a display. For example, detailed description regarding HDMI Standards is disclosed in NPL.